Anatase Identification Guide

What Anatase Looks Like

Anatase is one of three natural forms of titanium dioxide (TiO2), crystallizing in the tetragonal system. Its most distinctive habit is the steep, double-ended (dipyramidal) crystal that looks like two sharp four-sided pyramids joined base to base — almost a tiny dark "acorn" or spindle. Color is typically deep blue to indigo, brown, black, or honey-yellow, and luster ranges from adamantine (diamond-like) to brilliant metallic-adamantine. Crystals are usually small (millimeter to centimeter scale) and transparent to opaque.

Step-by-Step Field-ID Checklist

1. Look at crystal shape — sharp, steeply pyramidal tetragonal crystals are the giveaway.
2. Note the luster — bright adamantine to splendent metallic, much brighter than ordinary silicates.
3. Check the color — blue-black, brown, or yellow on a small isolated crystal sitting on quartz, feldspar, or schist.
4. Test hardness — Mohs 5.5–6; it scratches glass with difficulty and is scratched by a steel file.
5. Take a streak — colorless to pale yellow or off-white, despite the dark crystal color.

Key Diagnostic Tests

• Mohs hardness: 5.5–6.
• Streak: white to pale yellow.
• Cleavage: good basal and pyramidal cleavage (distinct, unlike rutile's prismatic cleavage).
• Specific gravity: ~3.8–3.9 — high, but lower than rutile (~4.2–4.3), a useful separator.
• Non-magnetic, inert to acid.

Common Look-Alikes

• Rutile (TiO2 polymorph): typically forms slender prismatic or needle-like crystals and golden-red striated prisms, is harder (Mohs 6–6.5) and denser (SG ~4.2). Anatase's steep bipyramids and lower density distinguish it.
• Brookite (TiO2 polymorph): orthorhombic, forming tabular or bladed brown crystals rather than steep bipyramids.
• Cassiterite (SnO2): much denser (SG ~7), with adamantine luster but blockier crystals and a far higher heft.
• Dark spinel or magnetite: magnetite is magnetic and gives a black streak; anatase is non-magnetic with a pale streak.

Where It Is Found

Anatase is a typical alpine-fissure and hydrothermal-vein mineral, found on quartz and feldspar in cavities of gneiss and schist, and as a detrital grain in sandstones. Classic crystallized specimens come from the Alps (Switzerland, France, Italy), Brazil (Minas Gerais), Norway, and the U.S. (Massachusetts, Colorado). Fine sharp bipyramids on matrix are prized by collectors.